violence flared across afghanistan today. four nato troops were killed in bombings in the east and south. and, eleven afghan policemenç died in separate attacks. amid the killings, general david petraeus-- commander of u.s. and nato troops in afghanistan-- handed over his duties. he is leaving to lead the central intelligence agency. his replacement is u.s. marine corps general john allen. >> it is my intention to maintain the momentum of this campaign, this great campaign on which we have embarked. i will continue to support in every way possible, the recruiting, the training, preparation and equipping and the fielding and the employment of the afghaf oational security forces.ç >> sreenivasan: allen's tenure began just a day after taliban insurgents claimed another high- profile assassination. a close aide to afghan president hamid karzai was killed sunday in a gunbattle at his home in kabul. it followed the murder of karzai's half-brother last week. for more on afghanistan we turn to pam constable, who covers south asi